The invention relates to a method and an apparatus for regulating the fuel-air mixture provided to an internal combustion engine. The regulation includes the supply of supplementary air to be added to a fuel-air mixture generated in a mixture generator in dependence on the operational state of the internal combustion engine.
In a known method of this kind, an oxygen sensor measures the oxygen content of the exhaust gases. The sensor is preferably an oxygen-ion conducting solid electrolyte, e.g., Zirconium dioxide. The output signal from the sensor is fed to a controller which sets an air bypass valve. If the oxygen content of the exhaust is low, indicating a rich mixture, the bypass valve is opened and the mixture is leaned out. Since this method employs only the oxygen sensor signal for setting the bypass valve, the relative adjustment of the fuel-air mixture is substantially smaller for large air flow rates (open throttle) than for small air flow rates.
In another known method of this type, the oxygen content of the exhaust gases is again monitored and additional air is metered out by a bypass valve in dependence on the exhaust gas oxygen content. In that system, an electronic controller determines the throttle position as well as the engine rpm to define a basic setting of the bypass valve while the oxygen content in the exhaust gases superimposes a further opening motion of the valve. Thus, fuel mixture preparation is independent of air flow. This type of known regulation requires a fairly substantial and expensive controller. Furthermore, the quantity of actually aspirated fuel-air mixture can be determined only by the throttle valve position together with the rpm signal or the vacuum in the induction tube. Thus, two measured quantities are required in order to find the parameter whose exact measurement is most important and that parameter is then processed to provide a setting signal for the bypass throttle valve.